1. Field of the Invention
The present invention relates to a paper feeding apparatus having a sucker for holding, by suction, an upper surface of printing paper placed on a paper tray, and transporting the paper to a printing machine.
2. Description of the Related Art
In such a paper feeding apparatus, printing paper with one surface thereof already printed may be placed one sheet over another on the paper tray to have the other surface printed. At this time, the printing paper has an image-bearing central area thereof swelling upward, owing to the thickness of ink, relative to marginal areas. This results in a phenomenon that the upper surface of the printing paper is convexed. When the upper surface of the printing paper is convexed in this way, the sucker cannot properly hold the printing paper by suction. In the conventional paper feeding apparatus, therefore, wedge-shaped spacers are inserted between the printing paper and paper tray to level the upper surface of the printing paper.
However, the curve of the upper surface of printing paper varies with the number of sheets of printing paper placed on the paper tray. The wedge-shaped spacers must be changed or removed in the course of continuous printing. However, it is difficult to change or remove the spacers while the printing machine is performing a printing operation.
It is also possible to damage printing paper or the printing machine when the wedge-shaped spacers are inserted to inappropriate positions, or when the spacers are not removed before completion of a printing operation.